2,3-Butanediol (2,3-BDO) is a multi-functional platform chemical that can be used to produce other bulk chemicals and synthesize diverse products, such as drugs, cosmetics, and industrial solvents (Celinska and Grajek, 2009; Syu, 2001).
More particularly, 2,3-BDO may be used in considerable industrial applications on important markets, as herein after summarized.

Two of the most interesting 2,3-BDO applications are the Methyl Ethyl Ketone (MEK solvent) and the butadiene (BDE), a major monomer in the manufacture of synthetic rubber and tires.
The traditional chemical synthesis of 2,3-BDO is faced the drawback of the petroleum deficiency and environmental pollution, whereas the manufacturing of 2,3-BDO is currently still growing by an annual rate of 4-7% (Jiayang et al., 2006).
Many chemicals that could only be produced by traditional chemical processes in the past can now have the potential to be generated biologically, using renewable resources (Danner & Braun, 1999; Hatti-Kaul et al., 2007). Microbial production of 2,3-BDO is one such example. Interest in this bioprocess has increased remarkably because 2,3-BDO has a large number of industrial applications, as above-mentioned, and microbial production will alleviate the dependence on oil supply for the production of platform chemicals (Celmska & Grajek, 2009; Wu et al., 2008). Saccharomyces cerevisiae is an especially well suited platform for such bioprocesses (Nielsen et al., 2013).
However, at the time being, the 2,3-BDO produced by microbial processes is a compound rarely used on an industrial scale, due to its high production costs notably linked to poor production yield. The chemical industry uses indeed preferentially other C4 chemicals compounds, such as 1,4-BDO and succinic acid.
Regarding the microbial production of 2,3-BDO, most studies used bacteria, such as Klebsiella pneumonia, Klebsiella oxytoca, Enterobacter aerogenes, and Paenibacillus polymyxa to produce 2,3-BDO (Cho et al., 2012; Han et al., 2013; Hassler et al., 2012; Jung et al., 2012). While these bacteria are capable of producing 2,3-BDO with high yields and productivities, they are however classified as pathogenic bacteria so that large-scale fermentation might be difficult in terms of safety and industrialization (Celinska and Grajek, 2009).
2,3-BDO production by a GRAS (i.e. generally recognized as safe) microorganism would thus be desirable. Yeast, and more particularly Saccharomyces cerevisiae, is an appropriate microorganism in this context. S. cerevisiae is known to produce 2,3-BDO naturally, but the yield and productivity of 2,3-BDO production are poor. Ethanol production is indeed the most obvious barrier for the efficient 2,3-BDO production in S. cerevisiae because pyruvate, a key intermediate, is preferentially used for producing ethanol rather than 2,3-BDO.
In order to minimize ethanol production and maximize 2,3-BDO production, a pyruvate decarboxylase (Pdc)-deficient mutant has been utilized for 2,3-BDO production. However, Pdc-deficient strains have potential defects for industrial fermentations (Flikweert et al., FEMS Microbiology Letters 174, 1999 73-79).
WO 2013/076144, WO 2011/040901 and US 2011/0124060 discloses non-naturally occurring microorganism having an improved 2,3-BDO pathway. Ethanol and acetate production pathways being disrupted, US 2011/0124060 and WO 2013/076144 describe that it leads to an unbalanced redox state to which the proposed solution consists to increase the activity of a NADH-dependent enzyme and, possibly, the pool of NAD+.
In Soo-Jung Kim et al. (Bioresource Technology 146 (2013) 274-281) was constructed Pdc-deficient strain and evolved for growing on glucose. The evolved Pdc-deficient strain was genotyped to identify necessary genetic changes which enable the Pdc-deficient strain to grow on high glucose concentration. However, these strains grow slowly has compared to strains that have retain some pdc activity. Subsequently, the 2,3-BDO biosynthetic pathway from Bacillus subtilis was introduced into the evolved Pdc-deficient strain to produce 2,3-BDO from glucose efficiently in S. cerevisiae. This strain is displayed as producing 96.2 g/L after 244 h cultivation, with a 2,3-BDO yield (0.28 g 2,3-BDO/g glucose) and volumetric productivity (0.39 g 2,3-BDO/Lh−1). However, this 2,3-BDO yield appears not appropriate to be economically viable on an industrial point of view.
Therefore, for obvious reasons, to improve the production of 2,3-BDO through microbial processes, and more particularly of the conversion of pyruvate to 2,3-BDO, remains a constant aim. More particularly, there is still a need in a stable recombinant microorganism having an enhanced production yield of 2,3-butanediol, in particular compatible with industrialization requirements.